13,104 research outputs found
Conceptual nonorthogonal gyro configuration for guidance and navigation
Nonorthogonal sensor configuration using six single-degree-of-freedom inertial reference gyroscopes and a complete data processing and self-contained failure detection-and-isolation mechanism provides redundant capabilities to guidance and navigation systems. This system has been formulated in a strap-down configuration to attain maximum redundancy
SIRU development. Volume 1: System development
A complete description of the development and initial evaluation of the Strapdown Inertial Reference Unit (SIRU) system is reported. System development documents the system mechanization with the analytic formulation for fault detection and isolation processing structure; the hardware redundancy design and the individual modularity features; the computational structure and facilities; and the initial subsystem evaluation results
Strapdown system Performance Optimization Test evaluations (SPOT), volume 2
A three axis inertial system is packaged in an Apollo gimbal fixture for fine grain evaluation of strapdown system performance in dynamic environments. These evaluations have provided information to assess the effectiveness of real-time compensation techniques and to study system performance tradeoffs to factors such as quantization iteration rate. The strapdown performance and tradeoff studies conducted in this program are discussed
Preferential attachment during the evolution of a potential energy landscape
It has previously been shown that the network of connected minima on a
potential energy landscape is scale-free, and that this reflects a power-law
distribution for the areas of the basins of attraction surrounding the minima.
Here, we set out to understand more about the physical origins of these
puzzling properties by examining how the potential energy landscape of a
13-atom cluster evolves with the range of the potential. In particular, on
decreasing the range of the potential the number of stationary points increases
and thus the landscape becomes rougher and the network gets larger. Thus, we
are able to follow the evolution of the potential energy landscape from one
with just a single minimum to a complex landscape with many minima and a
scale-free pattern of connections. We find that during this growth process, new
edges in the network of connected minima preferentially attach to more
highly-connected minima, thus leading to the scale-free character. Furthermore,
minima that appear when the range of the potential is shorter and the network
is larger have smaller basins of attraction. As there are many of these smaller
basins because the network grows exponentially, the observed growth process
thus also gives rise to a power-law distribution for the hyperareas of the
basins.Comment: 10 pages, 10 figure
An Independent Calibration of Stellar Ages: HST Observations of White Dwarfs at V=25
The white dwarf luminosity function of a stellar cluster will have a sharp
truncation at a luminosity which is determined by the time since formation of
the first white dwarfs in that cluster. Calculation of the dependence of this
limiting luminosity on age requires relatively well-understood physics and is
independent of stellar evolutionary models. Thus, measurement of the
termination of the white dwarf luminosity function provides an independent
method to determine the age of a cluster, and thereby to calibrate stellar
evolutionary ages. We have obtained HST WFPC2 data in two open clusters,
identified the white dwarf sequence, and proved the feasibility of this
approach, by detecting white dwarfs to V=25. Much deeper data are feasible.
From our present limited data, we show that degenerate cooling ages are not
consistent with some published isochrone ages for clusters with ages of order
1Gyr.Comment: 5 pages plus 3 figures ps format, paper in press in MNRAS: previous
attempt lost the tex
Cooperative heterogeneous facilitation: multiple glassy states and glass-glass transition
The formal structure of glass singularities in the mode-coupling theory (MCT)
of supercooled liquids dynamics is closely related to that appearing in the
analysis of heterogeneous bootstrap percolation on Bethe lattices, random
graphs and complex networks. Starting from this observation one can build up
microscopic on lattice realizations of schematic MCT based on cooperative
facilitated spin mixtures. I discuss a microscopic implementation of the F13
schematic model including multiple glassy states and the glass-glass
transition. Results suggest that our approach is flexible enough to bridge
alternative theoretical descriptions of glassy matter based on the notions of
quenched disorder and dynamic facilitation.Comment: 4 pages, 2 figure
An N.Q.R. study of some inorganic compounds
Nuclear quadrupole resonance (n.q.r.) spectroscopy is a solid state technique which, when applied to samples containing quadrupolar nuclei, can elucidate fine structural differences and internal electronic distribution. It has-been applied to a variety of inorganic compounds containing the quadrupolar nuclei, chlorine and cobalt, (i.e. (^35) CL and (^59Co). In order to remove spurious responses on a Robinson type n.q.r. spectrometer, apparatus has been constructed to generate sinusoidal magnetic modulation. Monomeric and chain- structures have been proposed for members of a series of complexes between zinc chloride and ethers. Marked asymmetry in the electric field gradient at chlorine has been reported for tetrachlorides of group IV. Although distortion of the molecules in the solid and disorder in the lattice are likely to produce asymmetry, it is suggested, that pπ-dπ bonding makes a major contribution. Such bonding is postulated for the tetrachlorides above carbon tetrachloride. Zeeman line shape studies on thionyl chloride and tetrachlorophenyl phosphorane have yielded estimates for TT-bonding in the bonds to chlorine. A variable temperature study of the (^59)Co quadrurole resonances of π-cyclopentadienyl cobalt dicarbonyl has revealed the absence of phase changes between 77K and 260K.
Alternative determinism principle for topological analysis of chaos
The topological analysis of chaos based on a knot-theoretic characterization
of unstable periodic orbits has proved a powerful method, however knot theory
can only be applied to three-dimensional systems. Still, the core principles
upon which this approach is built, determinism and continuity, apply in any
dimension. We propose an alternative framework in which these principles are
enforced on triangulated surfaces rather than curves and show that in dimension
three our approach numerically predicts the correct topological entropies for
periodic orbits of the horseshoe map.Comment: Accepted for publication as Rapid Communication in Physical Review
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